The invention relates to solid particles containing metal peroxides and more particularly alkaline earth metal peroxides. It also relates to a process for their preparation and a process for their use for the amendment of soils, especially in agriculture, in horticulture and in sylviculture.
Metal peroxides, such as alkaline earth metal peroxides, constitute very valuable sources of oxygen for various uses. Thus, it is known to amend soils by incorporating solid particles of calcium peroxide therein, from the purpose of obtaining a slow release of oxygen. The oxygen is absorbed by the roots of the plants and promotes their growth (Japanese Patent Application 51/141,265 filed on May 20, 1975 in the name of Nippon Peroxide K.K.).
This slow and continuous supply of oxygen is particularly desirable for crops grown under anaerobic conditions. This is the case when the soils are insufficiently aerated because they are impregnated or filled with water, or even completely flooded, or alternatively because the outer layer has a reduced porosity, for example because of the settling of the earth. This is also the case with soils which contain a large proportion of constituents with a high biochemical oxygen demand (BOD). These constituents can result from the decomposition of organic substances, for example following the use of herbicides, or alternatively from the decomposition of refuse from earlier harvests on unploughed earth.
When they are in the form of anhydrous solid particles, alkaline earth metal peroxides, and more particularly calcium peroxide, decompose only very slightly. On the other hand, in the presence of moisture, calcium peroxide decomposes rapidly, releasing its active oxygen. This decomposition is accelerated if the medium is acid, as can arise naturally in soils or as can result from the presence of certain additives normally used in agriculture, horticulture or sylviculture, such as certain fertilizers. Under these conditions, peroxides in the form of particles do not decompose sufficiently slowly to ensure a continuous supply of oxygen, from the period of germination of the seeds to the period of growth of the plant, or sufficiently completely to allow the utilisation of all the oxygen which is available in principle.
To reduce the rate of decomposition of calcium peroxide when it is used for the treatment of water, it has been proposed to coat it by means of water-insoluble coating agents (European Patent Application 78/200,306 filed on Nov. 15, 1978 in the name of Interox). However, some of these insoluble coating agents form a protective layer which is so effective that it is difficult to recover all the oxygen which is available in principle.